Scraper winch motors on South African gold mines-an investigation into their failure

This paper investigates some of the probable reasons for failure of squirrel cage induction machines driving scraper winches in South African gold mines. The paper shows the results of load current and voltage unbalance measurements that were recorded on winches in operation. There are further measurements showing the presence of time harmonics in the supply to some winches. More importantly, the paper shows the measured torque-speed curve of a typical scraper winch machine. This curve seems to indicate that there are significant space harmonics present in the air-gap of the winches, which may be causing rotor heating and premature bearing failure